Popular ethical food labels which claim to reassure consumers of high standards of animal welfare are criticised tonight in a TV programme which shows shocking scenes of neglect on some farms including ducks being punched, kicked and thrown around by staff.

Among the brands singled out is the Freedom Food scheme, launched by Britain's largest animal welfare organisation, the RSPCA , and used to certify meat products sold at a premium through Britain's main supermarket chains.

Secret filming at one Norfolk farm which claims to operate "the very highest standards of welfare" and participates in the Freedom Food scheme, reveals numerous injured and diseased turkeys, with sightings last month of rotting corpses in a "dead bin" which was not sealed, in breach of the government's emergency control order .

An investigation by Tonight with Trevor McDonald - being screened on ITV this evening - uses secret filming by an animal welfare group to reveal apparent maltreatment of animals at four Norfolk farms where thousands of animals are slaughtered every year and eventually supplied to supermarkets as "ethically produced" food which can cost at least twice as much as the non-ethical equivalent.

A former RSPCA council member claims on the programme that the inspection back-up provided by the RSPCA for the Freedom Food scheme is flawed because it employs too few people.

One in 20 farm animals in Britain is reared under the Freedom Food scheme, but there are only 10 full-time officials to police it which means that farms can go up to 15 months without an inspection. The latest findings follow investigations by BBC Watchdog and Channel 4 Dispatches, in which animal rights campaigners warned that Freedom Food was effectively large-scale industrial farming.

It shows several dead ducks which appear not to have been removed properly - including one that looks flattened - alongside filthy drinking water and a distressed duck suffering from torticollis, a condition involving a twisted neck.

The farm was owned by AE Button, a subsidiary of Kerry Foods, at the time of filming last spring, but is now owned by Green Label, whose director told Tonight he has shut it down. Cherrydene farm in Bergh Apton, Norfolk, is not part of the Freedom Food scheme but produced ducklings for Manor Farm Ducklings which supplies to Morrisons, Asda and Macro. The stills of footage last autumn show ducks being rounded up and crated. One member of staff punches a duck while others pick them up by the throat, throw them and kick them.

At Mary farm, Rakheath, Norfolk, where pigs reared under the Freedom Food scheme are supplied to Sainsbury's and Waitrose, footage shows pigs in wet and heavily soiled conditions with no straw or dry, comfortable rest area.

Hall farm in Caston, Norfolk, rears turkeys under the Freedom Food scheme for Traditional Norfolk Poultry, which supplies Asda and the Co-op, but filming revealed clear breaches of the government's regulations on disposal of dead birds. The farm said it is ceasing turkey production.

In an interview on the programme, Celia Hammond, a former RSPCA council member, says the organisation does not employ enough people to inspect farms properly and urges the RSPCA to withdraw from the scheme: "They can't adequately monitor the number of animals."

Last night an RSPCA spokesman said the farms involved had been suspended from the scheme and that it took the allegations very seriously.

The RSPCA's director general, Jackie Ballard, admitted in the programme: "There were some examples of very poor animal welfare on those farms and of animals that were very clearly suffering and that's not good enough.

"We have the most monitoring of any of the labelling schemes that there are in this country. But we don't sit on a farm 24 hours a day monitoring, so inevitably sometime things will go wrong."

She said the five freedoms were "aspirations" rather than guarantees: "The Freedom Food scheme, you know what our aspiration is? Our aspiration is that that becomes legal minimum standards."